Ultramafic Alkaline Rocks of Kepino Cluster, Arkhangelsk, Russia: Different Evolution of Kimberlite Melts in Sills and Pipes

To provide new insights into the evolution of kimberlitic magmas, we have undertaken a detailed petrographic and mineralogical investigation of highly evolved carbonate–phlogopite-bearing kimberlites of the Kepino cluster, Arkhangelsk kimberlite province, Russia. The Kepino kimberlites are represented by volcanoclastic breccias and massive macrocrystic units within pipes as well as coherent porphyritic kimberlites within sills. The volcanoclastic units from pipes are similar in petrography and mineral composition to archetypal (Group 1) kimberlite, whereas the sills represent evolved kimberlites that exhibit a wide variation in amounts of carbonate and phlogopite. The late-stage evolution of kimberlitic melts involves increasing oxygen fugacity and fluid-phase evolution (forming carbonate segregations by exsolution, etc.). These processes are accompanied by the transformation of primary Al- and Ti-bearing phlogopite toward tetraferriphlogopite and the transition of spinel compositions from magmatic chromite to magnesian ulvöspinel and titanomagnetite. Similar primary kimberlitic melts emplaced as sills and pipes may be transitional to carbonatite melts in the shallow crust. The kimberlitic pipes are characterised by low carbonate amounts that may reflect the fluid degassing process during an explosive emplacement of the pipes. The Kepino kimberlite age, determined as 397.3 ± 1.2 Ma, indicates two episodes of ultramafic alkaline magmatism in the Arkhangelsk province, the first producing non-economic evolved kimberlites of the Kepino cluster and the second producing economic-grade diamondiferous kimberlites

Sheared peridotite xenolith from the V. Grib kimberlite pipe, Arkhangelsk Diamond Province, Russia: Texture, composition, and origin

The petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk Diamond Province, Russia) was studied. Based on petrographic characteristics, the peridotite xenolith reflects a sheared peridotite. The sheared peridotite experienced a complex evolution with formation of three main mineral assemblages: (1) a relict harzburgite assemblage consist of olivine and orthopyroxene porphyroclasts and cores of garnet grains (Gar1) with sinusoidal rare earth elements (REE) chondrite C1 normalized patterns; (2) a neoblastic olivine and orthopyroxene assemblage; (3) the last assemblage associated with the formation of clinopyroxene and garnet marginal zones (Gar2). Major and trace element compositions of olivine, orthopyroxene, clinopyroxene and garnet indicate that both the neoblast and clinopyroxene-Gar2 mineral assemblages were in equilibrium with a high Fe-Ti carbonate-silicate metasomatic agent. The nature of the metasomatic agent was estimated based on high field strength elements (HFSE) composition of olivine neoblasts, the garnet-clinopyroxene equilibrium condition and calculated by REE-composition of Gar2 and clinopyroxene. All these evidences indicate that the agent was a high temperature carbonate-silicate melt that is geochemically linked to the formation of the protokimberlite melt

Few-Layer Graphene as an Efficient Buffer for GaN/AlN Epitaxy on a SiO2/Si Substrate: A Joint Experimental and Theoret-ical Study

Single-layer (SLG)/few-layer (FLG) and multilayer graphene (MLG) (>15 layers) samples were obtained using the CVD method on high-textured Cu foil catalysts. In turn, plasma-assisted molecular beam epitaxy was applied to carry out the GaN graphene-assisted growth. A thin AlN layer was used at the initial stage to promote the nucleation process. The effect of graphene defectiveness and thickness on the quality of the GaN epilayers was studied. The bilayer graphene showed the lowest strain and provided optimal conditions for the growth of GaN/AlN. Theoretical studies based on the density functional theory have shown that the energy of interaction between graphene and AlN is almost the same as between graphite sheets (194 mJ/m2). However, the presence of vacancies and other defects as well as compression-induced ripples and nitrogen doping leads to a significant change in this energy

Few-Layer Graphene as an Efficient Buffer for GaN/AlN Epitaxy on a SiO2/Si Substrate: A Joint Experimental and Theoret-ical Study

Single-layer (SLG)/few-layer (FLG) and multilayer graphene (MLG) (>15 layers) samples were obtained using the CVD method on high-textured Cu foil catalysts. In turn, plasma-assisted molecular beam epitaxy was applied to carry out the GaN graphene-assisted growth. A thin AlN layer was used at the initial stage to promote the nucleation process. The effect of graphene defectiveness and thickness on the quality of the GaN epilayers was studied. The bilayer graphene showed the lowest strain and provided optimal conditions for the growth of GaN/AlN. Theoretical studies based on the density functional theory have shown that the energy of interaction between graphene and AlN is almost the same as between graphite sheets (194 mJ/m2). However, the presence of vacancies and other defects as well as compression-induced ripples and nitrogen doping leads to a significant change in this energy